1. Field of Invention
This invention relates to a thermal head comprising a heating resistive element formed in the direction of the end surface of a substrate thereof and usable in printing apparatus, and a method of manufacturing the same.
2. Description of the Prior Art
A conventional thermal head, such as shown in FIG. 1, generally comprises a substrate and a heating resistive element formed on the end portion of the substrate. In FIG. 1, the thermal head comprises a heating resistive element 2 formed on the end surface of a substrate 1 and electrode layers 3 and 4 laminated on opposite surfaces of the substrate with a part of each layer 3,4 overlapping the heating resistive element 2. This structure can provide a thermal head of high thermal efficiency, because the heating portion of the heating resistive element 2 comes into close contact with the recording paper or the like of a printer in which the thermal head may be used. Furthermore since the end portions of the substrate 1 can be shaped more evenly than the top or bottom portions, a plurality of heating resistive element 2 can be brought uniformily into contact with the recording paper or the like, with the result that high quality printing can be attained.
However, this conventional thermal head has the following disadvantages and deficiencies, which may be due to the electrode layers 3,4 being formed on both sides of substrate 1 in the manner depicted.
(1) It is impossible to form both electrode layers 3,4 on the respective sides of the substrate simultaneously. Thus, exact positioning of the electrode layers 3,4 in two steps, which is not simply, is necessitated.
(2) When a material such as ceramic (which is difficult to form a hole therein) is used for substrate 1, the wiring of, for example, lead wires must be conducted on another substrate, which makes it difficult to build a drive IC and other elements in the structure.
(3) Since the size of a printing dot (the length of the heating resistive element 2) is determined by the thickness of substrate 1, it is desirable to make substrate 1 as thin as possible for the purpose of improving the resolution of recording. On the other hand, if substrate 1 is too thin, the mechanical strength is weakened, which makes manufacturing of the head difficult.
(4) Since heating resistive element 2 is formed to envelop the end portion of substrate 1, there may be a break in the resistive element at the parts where the element folds around the edge portion of substrate 1.
Thus, the conventional thermal heads leave much to be desired.